Megacity

A megacity is a very large city, typically with a population of more than 10 million people. The United Nations Department of Economic and Social Affairs (UN DESA) in its 2018 "World Urbanization Prospects" report defines megacities as urban agglomerations with over 10 million inhabitants. A University of Bonn report holds that they are "usually defined as metropolitan areas with a total population of 10 million or more people". Elsewhere in other sources, from five to eight million is considered the minimum threshold, along with a population density of at least 2,000 per square kilometre. The terms conurbation, metropolis, and metroplex are also applied to the latter.

The total number of megacities in the world varies between different sources and their publication dates. The world had 32 according to EU Global Human Settlement Layer (in 2024), 33 according to UN DESA (in 2018), 39 according to the OECD, 44 according to Demographia (in 2023), and 45 according to CityPopulation.de (in 2023). In total, 53 unique places are mentioned as megacities across these sources. A good percentage of these urban agglomerations are in China and India. The other four countries with more than one megacity are Brazil, Japan, Pakistan, and the United States. African megacities are present in Nigeria, Egypt, South Africa, Angola and the DRC; European megacities are present in Russia, France, the United Kingdom, and Turkey (also in Asia); megacities can be found in Latin America in the countries of Brazil, Mexico, Colombia, Peru, and Argentina.

Some sources identify the Greater Tokyo Area as the largest megacity in the world, while some others give the title to the Pearl River Delta in China.

Urban Metric System

Template:Rewrite section Since, presently, urban data are based on arbitrary definitions that vary from country to country and from year or census to the next, making them difficult to compare, an Urban Metric System (UMS) has been conceived that could correct the problem, since it allows computing the urban area limits and central points, and it can be applied in the same way to all past, present and future population and job distributions.

It is based on vector field calculations obtained by assuming that, in a given space, all inhabitants and jobs exert the same attractive force A and repulsive force R. The net force (A - R) exerted by each inhabitant or job is given by [1/(1 + d)] - [1/( β + d/2)], where d = distance and β is the only parameter.

UMS distinguishes the following types of urban areas(including "patropolises" that are tantamount to "megacities"), each type corresponding to a given value of β:

	Urban area	Distance at which the attractive force = the repulsive force	Value of β
1	Central city	10 km	6
2	Agglomeration	20 km	11
3	Metropolis	40 km	21
4	Patropolis	80 km	41
5	Megalopolis	160 km	81
6	Urban system	320 km	161
7	Urban macrosystem	640 km	321
8	Continental system	1,280 km	641
9	Intercontinental system	2,560 km	1,281
10	World system	5,120 km	2,561

UMS has been applied to some Canadian cases since 2018, but the data presented in this article are still based on the various existing national definitions, which are disparate.

List of megacities

Megacity	Image	Country	Region	Estimated population
				Citypopulation.de (2025)	Demographia (2023)	GHSL (2024)	UN DESA (2018)	OECD (2020)
Bangalore	File:UB City.jpg	India	South Asia	14,700,000	15,257,000	15,178,533	11,440,000	14,253,019
Bangkok	File:0008871 - Krung Thep Bridge 001.jpg	Thailand	Southeast Asia	21,800,000	18,884,000	19,048,032	10,156,000	18,601,400
Beijing	File:Skyline of Beijing CBD with B-5906 approaching (20211016171955).jpg	China	East Asia	21,500,000	18,883,000	18,150,576	19,618,000	20,738,738
Bogotá	File:Bogota z veže Colpatria (34432642862).jpg	Colombia	South America	10,600,000	10,252,000	10,419,361	10,574,000	10,544,590
Buenos Aires	File:High-rises of Puerto Madero (40022145164).jpg	Argentina	South America	16,800,000	15,748,000	14,179,912	14,967,000	14,590,526
Cairo	File:Cropped Cairo.jpg	Egypt	Template:Sort	22,800,000	22,679,000	25,230,325	20,076,000	27,925,433
Changsha	File:Skyline with Xiang River.png	China	East Asia	11,500,000	5,065,000	3,246,971	4,345,000	4,009,195
Chengdu	File:雪山下的成都市天际线 Chengdu skyline with snow capped mountains.jpg	China	East Asia	18,100,000	15,016,000	5,609,627	8,813,000	9,768,500
Chennai	File:Victoria Public Hall and Chennai central aerial view.jpg	India	South Asia	12,900,000	11,570,000	11,466,400	10,456,000	11,528,915
Chongqing	File:重庆市渝中区半岛.jpg	China	East Asia	12,900,000	12,653,000	8,449,690	14,838,000	8,913,804
Delhi	File:Skyline at Rajiv Chowk.JPG	India	South Asia	35,700,000	31,190,000	31,422,508	28,514,000	33,495,554
Dhaka	File:Dhaka 14th March (32624769393).jpg	Bangladesh	South Asia	23,100,000	19,134,000	37,307,160	19,578,000	22,762,988
Dongguan	File:Dongguan in June 19, 2025 (1).jpg	China	East Asia	Combined with Guangzhou	10,753,000	Combined with Guangzhou	7,360,000	Combined with Guangzhou
Guangzhou	File:Guangzhou Twin Towers.jpg	China	East Asia	72,700,000	27,119,000	42,987,704	12,638,000	16,650,322
Hangzhou	File:20201012从钱塘江江面上空观看钱江新城.jpg	China	East Asia	14,600,000	9,618,000	6,387,064	7,236,000	9,013,951
Ho Chi Minh City	File:Saigon skyline night view.jpg	Vietnam	Southeast Asia	14,300,000	14,953,000	14,557,830	8,145,000	14,247,593
Hyderabad	File:Manjeera Trinity corporate building, KPHB.jpg	India	South Asia	11,700,000	9,797,000	9,455,230	9,482,000	9,706,886
Istanbul	File:View of Levent financial district from Istanbul Sapphire.jpg	Turkey	Europe West Asia	16,000,000	14,441,000	14,210,222	14,751,000	14,693,269
Jakarta	File:SCBD, Jakarta.jpg	Indonesia	Southeast Asia	29,500,000	35,386,000	40,545,126	10,517,000	32,513,588
Jieyang	File:Puning Urban Night View from Baierqiutian.jpg	China	East Asia	Combined with Shantou	2,516,000	10,579,303	-	13,891,202
Johannesburg	File:Johannesburg CBD.jpg	South Africa	Template:Sort	14,800,000	15,551,000	8,592,843	5,486,000	9,497,036
Karachi	File:Skyline view in Karachi after lockdown.jpg	Pakistan	South Asia	21,000,000	20,249,000	21,031,703	15,400,000	18,916,709
Kinshasa	File:Boulevard du 30 juin, Kinshasa.jpg	DR Congo	Template:Sort	16,300,000	13,493,000	12,945,683	13,171,000	10,077,694
Kolkata	File:EM Bypass Kolkata.jpg	India	South Asia	17,900,000	21,747,000	23,314,585	14,681,000	24,106,859
Lagos	File:Lagos skyline.jpg	Nigeria	Template:Sort	21,300,000	14,540,000	12,486,045	13,463,000	12,642,198
Lahore	File:Badshahi Mosquee, Lahore.jpg	Pakistan	South Asia	14,600,000	13,504,000	14,305,060	11,738,000	15,696,939
Lima	File:City of Lima, Peru.jpg	Peru	South America	12,000,000	10,556,000	10,828,104	10,391,000	10,496,389
London	File:City of London skyline from London City Hall - Sept 2015 - Crop Aligned.jpg	United Kingdom	Europe	15,100,000	10,803,000	10,408,333	9,046,000	13,475,297
Los Angeles	File:Los Angeles with Mount Baldy.jpg	United States	North America	17,100,000	15,587,000	13,474,333	12,458,000	16,206,529
Luanda	File:Marginal de Luanda HD Dji Mavic 3 Classic - By Délcio Geovany Borges.jpg	Angola	Template:Sort	9,650,000	10,914,000	11,672,134	7,774,000	10,212,263
Metro Manila	File:Makati Guadalupe-Poblacion skyline with Paco, Quirino (Manila; 12-23-2023).jpg	Philippines	Southeast Asia	27,800,000	24,156,000	25,921,189	13,482,000	27,327,889
Mexico City	File:Ciudad.de.Mexico.City.- Paseo.Reforma.Skyline CDMX 2016 (cropped).jpg	Mexico	North America	25,400,000	21,905,000	17,639,164	21,581,000	19,229,491
Moscow	File:Business Centre of Moscow 2.jpg	Russia	Europe	18,800,000	17,878,000	14,384,082	12,410,000	17,217,606
Mumbai	File:ওরলির গগনরৈখিক দৃশ্য.jpg	India	South Asia	27,600,000	25,189,000	20,453,270	19,980,000	23,435,141
Nagoya	File:Meieki from Heiwa Park Aqua Tower.jpg	Japan	East Asia	10,500,000	9,439,000	7,721,742	9,507,000	9,853,994
New York City	File:A view of New York City with the Empire State Building and One World Trade Center from the Rockefeller Center.jpg	United States	North America	21,800,000	21,396,000	14,197,659	18,819,000	20,106,617
Osaka	File:Nakanoshima Skyscrapers in 201504 001.jpg	Japan	East Asia	17,700,000	14,916,000	12,653,994	19,281,000	16,866,788
Paris	File:Eiffel Tower from the Tour Montparnasse 3, Paris May 2014.jpg	France	Europe	11,500,000	11,108,000	9,328,385	10,901,000	11,249,025
Rhine-Ruhr	File:Aerial view of Essen.jpg	Germany	Europe	10,900,000	6,769,000	-	-	-
Rio de Janeiro	File:Aerial View of Flamengo 1.jpg	Brazil	South America	13,600,000	12,306,000	9,853,693	13,293,000	11,068,999
São Paulo	File:SP from Altino Arantes Building.jpg	Brazil	South America	22,600,000	21,486,000	19,485,158	21,650,000	21,671,857
Seoul	File:Seoul (South Korea).jpg	South Korea	East Asia	25,200,000	23,225,000	22,261,692	9,963,000	25,199,125
Shanghai	File:Shanghai skyline waterfront pudong 5166168 69 70.jpg	China	East Asia	41,600,000	24,042,000	30,678,616	25,582,000	30,504,083
Shenzhen	File:Shenzhen Skyline from Nanshan.jpg	China	East Asia	Combined with Guangzhou	17,778,000	Combined with Guangzhou	11,908,000	Combined with Guangzhou
Surabaya	File:Central Surabaya view taken from JW Marriott Surabaya.jpg	Indonesia	Southeast Asia	5,950,000	6,556,000	6,856,993	-	10,695,358
Suzhou	File:东方之门1.jpg	China	East Asia	Combined with Shanghai	6,091,000	11,540,430	6,339,000	13,458,006
Taipei	File:Taipei Skyline 2022.06.29.jpg	Taiwan	East Asia	10,100,000	9,662,000	9,686,521	-	10,048,037
Tehran	File:North of Tehran Skyline view.jpg	Iran	West Asia	16,800,000	13,382,000	9,363,124	8,896,000	13,563,316
Tianjin	File:Tianjin Skyline 2009 Sep 11 by Nangua 1.jpg	China	East Asia	11,700,000	10,047,000	7,330,648	13,215,000	8,963,397
Tokyo	File:Minato City, Tokyo, Japan.jpg	Japan	East Asia	41,200,000	37,785,000	33,155,907	37,468,000	36,697,549
Wuhan	File:Wuhan Yangtze River Bridge in 2020.jpg	China	East Asia	12,600,000	10,353,000	8,079,484	8,176,000	8,947,812
Xiamen	File:Amoy Skyscrapers 2018.jpg	China	East Asia	15,400,000	5,253,000	1,676,987	3,585,000	4,261,898
Xi'an	File:Xi'an erhuan southeast.JPG	China	East Asia	13,400,000	12,211,000	5,298,991	7,444,000	6,818,858
Zhengzhou	File:20211224 CBD of Zhengdong New Area.jpg	China	East Asia	10,300,000	11,068,000	5,126,112	4,940,000	6,381,637

History

The term "megacity" entered common use in the late 19th or early 20th centuries; one of the earliest documented uses of the term was by the University of Texas in 1904. Initially the United Nations used the term to describe cities of 8 million or more inhabitants, but now uses the threshold of 10 million. In the mid 1970s the term was coined by urbanist Janice Perlman referring to the phenomenon of very large urban agglomerations.

File:2020 1million cities.jpg

Map showing urban areas with at least one million inhabitants in 2020

In 1800, only 3% of the world's population lived in cities, a figure that rose to 47% by the end of the twentieth century. In 1950, there were 83 cities with populations exceeding one million; by 2007, this number had risen to 468, with 153 of them located in Asia. Among the 27 megacities with populations over 10 million globally, 15 were situated in Asia.

In 2010, UN forecasted that urban population of 3.2 billion would rise to nearly 5 billion by 2030, when three out of five, or 60%, of people would live in cities. This increase will be most dramatic on the least-urbanized continents, Asia and Africa. Surveys and projections indicate that all urban growth over the next 25 years will be in developing countries. One billion people, almost one-seventh of the world's population, now live in shanty towns. In many poor countries, overcrowded slums exhibit high rates of disease due to unsanitary conditions, malnutrition, and lack of basic health care. By 2030, over 2 billion people in the world will be living in slums. Over 90% of the urban population of Ethiopia, Malawi and Uganda, three of the world's most rural countries, already live in slums.

By 2025, Asia alone will have at least 30 megacities, including Mumbai, India (2015 population of 20.75 million people), Shanghai, China (2015 population of 35.5 million people), Delhi, India (2015 population of 21.8 million people), Tokyo, Japan (2015 population of 38.8 million people) and Seoul, South Korea (2015 population of 25.6 million people). The top eight provincial capital cities in China with urban areas exceeding 400 km²—Beijing, Shanghai, Tianjin, Guangzhou, Chongqing, Hangzhou, Wuhan, and Xi'an—accounted for 54.8% of the total urban area of all provincial capital cities in the country in 2015.

In Africa, Lagos, Nigeria has grown from 300,000 in 1950 to an estimated 21 million today.

Growth

File:Détail de la maquette de Rome à lépoque de Constantin (5839479770).jpg

Gismondi's model of Rome in the time of Constantine

For almost five hundred years, during the period of the Republic and later of the Empire, Rome was the largest, wealthiest, and most politically important city of the ancient world, rulling over Europe, Western Asia and Northern Africa. It is often stated that its population passed one million people by the end of the 1st century BC, however, it is debated about whether the population actually reached such a large size. Rome's population started declining in 402 AD when Flavius Honorius, Western Roman Emperor from 395 to 423, moved the government to Ravenna and Rome's population declined to a mere 20,000 during the Early Middle Ages, reducing the sprawling city to groups of inhabited buildings interspersed among large areas of ruins and vegetation.

Baghdad was likely the largest city in the world from shortly after its foundation in 762 AD until the 930s, with some estimates putting its population at over one million. Chinese capital cities Chang'an and Kaifeng also experienced huge population booms during prosperous empires. According to the census in the year 742 recorded in the New Book of Tang, 362,921 families with 1,960,188 persons were counted in Jingzhao Fu (京兆府), the metropolitan area including small cities in the vicinity of Chang'an. The medieval settlement surrounding Angkor, the one-time capital of the Khmer Empire which flourished between the 9th and 15th centuries, could have supported a population of up to one million people.

File:Trafalgar Square by James Pollard.jpg

During the 19th century, London was transformed into the world's largest city and capital of the British Empire.

From around 1825 to 1918 London was the largest city in the world, with the population growing rapidly; it was the first city to reach a population of over 5 million in 1900. In 1950, New York City was the only urban area with a population of over 10 million. Geographers had identified 25 such areas as of October 2005, as compared with 19 megacities in 2004 and only nine in 1985. This increase has happened as the world's population moves towards the high (75–85%) urbanization levels of North America and Western Europe.

Since the 2000s, the largest megacity has been the Greater Tokyo Area. The population of this urban agglomeration includes areas such as Yokohama and Kawasaki, and is estimated to be between 37 and 38 million. This variation in estimates can be accounted for by different definitions of what the area encompasses. While the prefectures of Tokyo, Chiba, Kanagawa, and Saitama are commonly included in statistical information, the Japan Statistics Bureau only includes the area within 50 kilometers of the Tokyo Metropolitan Government Offices in Shinjuku, thus arriving at a smaller population estimate. A characteristic issue of megacities is the difficulty in defining their outer limits and accurately estimating the populations.

Another list defines megacities as urban agglomerations instead of metropolitan areas. As of 2021, there are 28 megacities by this definition, like Tokyo. Other sources list Nagoya and the Rhein-Ruhr as megacities.

Challenges

Slums

File:Mumbai (5356346073).jpg

Mumbai's Dharavi slum is home to 1 million residents

According to the United Nations, the proportion of urban dwellers living in slums or informal settlements decreased from 47 percent to 37 percent in the developing world between 1990 and 2005. However, due to rising population, the absolute number of slum dwellers is rising and passed 1 billion in 2018. The increase in informal settlement population has been caused by massive migration, both internal and transnational, into cities, which has caused growth rates of urban populations and spatial concentrations not seen before in history. The majority of these are located in informal settlements which often lack sufficient quality housing, sanitation, drainage, water access, and officially recognized addresses. These issues raise problems in the political, social, and economic arenas. People who live in slums or informal settlements often have minimal or no access to education, healthcare, or the urban economy.

Crime

File:View over Complexo do Alemao (Favela) - From Igreja da Penha - Rio de Janeiro - Brazil - 03 (17556920491).jpg

Most murders in Rio de Janeiro, Brazil are gang related and happen in the favelas

As with any large concentration of people, there is usually crime. High population densities often result in higher crime rates, as visibly seen in growing megacities such as Karachi, Delhi, Cairo, Rio de Janeiro, and Lagos.

Homelessness

Megacities often have significant numbers of homeless people. The actual legal definition of homelessness varies from country to country, or among different entities or institutions in the same country or region.

In 2002, research showed that children and families were the largest growing segment of the homeless population in the United States, and this has presented new challenges, especially in services, to agencies. In the US, the government asked many major cities to come up with a ten-year plan to end homelessness. One of the results of this was a "Housing first" solution, rather than to have a homeless person remain in an emergency homeless shelter it was thought to be better to quickly get the person permanent housing of some sort and the necessary support services to sustain a new home. But there are many complications with this kind of program and these must be dealt with to make such an initiative work successfully in the middle to long term.

Traffic congestion

File:Ratchadamri to Pratunam.jpg

Bangkok is notorious for its traffic congestion.

Traffic congestion is a condition on road networks that occurs as use increases, and is characterized by slower speeds, longer trip times, increased pollution, and increased vehicular queueing. The Texas Transportation Institute estimated that, in 2000, the 75 largest metropolitan areas experienced 3.6 billion vehicle-hours of delay, resulting in 5.7 billion U.S. gallons (21.6 billion liters) in wasted fuel and $67.5 billion in lost productivity, or about 0.7% of the nation's GDP. It also estimated that the annual cost of congestion for each driver was approximately $1,000 in very large cities and $200 in small cities. Traffic congestion is increasing in major cities and delays are becoming more frequent in smaller cities and rural areas. It also can result in various issues, including economic losses, energy waste, air and noise pollution, and more.

Urban sprawl

File:South-Los-Angeles-110-and-105-freeways-Aerial-view-from-north-August-2014.jpg

A flat land area in the Greater Los Angeles Area in the U.S. state of California with houses, buildings, roads, and freeways. Areas constructed to capacity contribute to urban expansion.

Urban sprawl, also known as suburban sprawl, is a multifaceted concept, which includes the spreading outwards of a city and its suburbs to its outskirts to low-density, auto-dependent development on rural land, with associated design features that encourage car dependency. As a result, some critics argue that sprawl has certain disadvantages including longer transport distances to work, high car dependence, inadequate facilities (e.g. health, cultural. etc.) and higher per-person infrastructure costs. Discussions and debates about sprawl are often obfuscated by the ambiguity associated with the phrase. For example, some commentators measure sprawl only with the average number of residential units per acre in a given area. But others associate it with decentralization (spread of population without a well-defined center), discontinuity (leapfrog development), segregation of uses, etc.

Gentrification

Gentrification and urban gentrification are terms for the socio-cultural changes in an area as a result of wealthier people buying property in a less prosperous community. As living costs rise, lower-income residents are forced to move out of the community leading to an increase in average income, which in turn makes the area more desirable to other wealthier property or business owners, further pushing the living costs up. This process also tends to lead to a decrease in average family size in the area. This type of population change reduces industrial land use when it is redeveloped for commerce and housing.

Air pollution

File:Shanghai Smog.JPG

Air pollution in Shanghai, China

Air pollution is the introduction into the atmosphere of chemicals, particulate matter, or biological materials that cause harm or discomfort to humans or other living organisms, or damages the natural environment. This issue is particularly prevalent in developing nations. As part of the Global Environment Monitoring System, WHO and UNEP established an air pollution monitoring network that oversees 50 cities. Many urban areas have significant problems with smog, a type of air pollution derived from vehicle emissions from internal combustion engines and industrial fumes that react in the atmosphere with sunlight to form secondary pollutants that also combine with the primary emissions to form photochemical smog.

Energy and material resources

The sheer size and complexity of megacities gives rise to enormous social and environmental challenges. Whether megacities can develop sustainably depends to a large extent on how they obtain, share, and manage their energy and material resources. There are correlations between electricity consumption, heating and industrial fuel use, ground transportation energy use, water consumption, waste generation, and steel production in terms of level of consumption and how efficiently they use resources.

In fiction

Megacities are a common backdrop in dystopian science fiction, with examples such as the Sprawl in William Gibson's Neuromancer, and Mega-City One, a megalopolis of between 50 and 800 million people (fluctuations due to war and disaster) across the east coast of the United States, in the Judge Dredd comic. In Demolition Man a megacity called "San Angeles" was formed from the joining of Los Angeles, Santa Barbara, San Diego and the surrounding metropolitan regions following a massive earthquake in 2010. Fictional planet-wide megacities (ecumenopoleis) include Trantor in Isaac Asimov's Foundation series of books and Coruscant (population two trillion) in the Star Wars universe.

See also

• Economies of agglomeration
• Global city
• List of largest cities
• List of largest cities throughout history
• Megalopolis
• Urban sprawl